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I am pretty new to "real" welding and have basicly no experience. In the past I did a few things, with electric arc welding, but that doesn't count anymore.
I use brazing with silver solder for my hobby (RC modeling), to build scale airplanes like a Piper P18, in which the fuselage is made from thin walled (wall thickness 0.01" - 0.02") stainless steel tubes. Normaly brazing with silver solder has enough strenght to keep things together, except in areas with a lot of dynamic load, like the wing and elevator hinges or the gear and especially the the engine mount. Most of the professional modell builders did some kind of workaround in those areas instead the original solution, because they don't trust a brazed connection in those areas. Most of the people which I have asked, have said categorically "no" it is not possible to weld such kind of thin tubing. But these people were not welding specialist, so maybe, while welding technology is in progress, there might be new - and affordable - possiblities nowadays.

Anyhow, attached you will see some pictures to make it easier to understand what I am talking about.
I am thankfull for any help, advice and information, even negative !

Comment

I do a lot of tig welding and the problems that I see in welding in your application would be torch handling under such a miniature environment and control of heat at very low amperages..... not saying it cannot be done... but see it as pretty challenging...
if you try the TIG route... the best torch from my viewpoint would be something like a WP-50 and for power supply.. it could even be a well regulated DC bench supply or one of the baby inverter welders like the Thermal Arc 95S or Harbor Freight 80amp types..... you will be working under 20 amps..... (something very controllacle at the lower end) this will take quite a bit of experimentation... and no small amount of skill... plus.. some dollar investment.... But it is doable if you have the determination.... not to mention eyesight and a good magnifier under your welding helmet...

Another approach may be using a higher silver content HARD solder with a mod of the critical joints.. possibly adding some gusseting or otherwise increasing the surface area of the joints and spreading out the stresses from point loads to distributed??

One approach that may be viable for your application might be to use a micro-tig torch like a wp-50 to apply one of the high strength... high temperature brazing alloys.... that hybrid method may give you the best of both worlds....

Bob...
as far as finding them... lots of places have em... here is a sample from Baker's..... (get the rubber hose not the vinyl it is lots more flexable for just a few bucks more...)

The whole fuselage was brazed with Harris Safety Silver 56% (which is the highest silver content I have seen). Every piece was cleaned with sandpaper and Aceton bevor brazing. I think the fuselage is strong enough, which has already being proofed by other builders who used the same technic.

TIG welding should only be used (if possible) for those components who under higher dynamic load. Which as an example means , welding a hinge from 0.039" stainless steel to a stainless steel tube with a wall thikness of 0.02".

In the picture you can see the rear landing gear fitting, that will be brazed or welded to the fuselage. It has to withstand the load from the wing strut and also the load from the landing gear. I can not imagine that this will work out with brazing. Easy to imagine what happen if this connection fails.

Anyway, it sounds like, let's get some TIG welding equipment, like you mentioned above and test test test test......maybe it will work, maybe it will only burn wholes in the tubes......

I will read the information about Micro Tig, after that, I will probably have some more questions..

Comment

Your engine choice is delightful .... looks like a miniature Franklin 2A-120 (O-120) Twin..... Guess they do not make miniature O-320 clones....

Wonderful project

some additional thoughts.... if that hinge is to be laid on top of other joints that have already been silver soldered then you will have precluded Tig Welding on that spot... as you will draw out the solder from the previously soldered ones.... you could however solder them using jewelry practice of using the next softer grade of silver solder

Hard
Medium
Soft

each softer grade melts at a lower temp allowing you to layer several items in steps without damaging the one done before....

please keep us posted... if you like PM me and I can probably help you with some sources....

Comment

I've been using 1/16th filler wire on mine, you probably want to hunt down something a bit smaller in diameter. I know there's .035" filler available, we had some at the last job I worked at. They may have had even smaller stuff, might have been .020" wire. That was at an aircraft manufacturing machine shop though. I never realized there were so many different types of filler metals until I worked there for a few years. Mostly Ti and inconel, but they did have several (8 or 9 at least) grades of stainless. Lots of other stuff that I had absolutely no clue what it was for, they just had numbers on it.

Those guys made my welds look like a pre-schooler scribbling with a crayon as opposed to a fine painting when compared to theirs.